Boaters are on, some oddly off (7)
I believe the answer is:
oarsmen
'boaters' is the definition.
(I know this)
'are on some oddly off' is the wordplay.
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
'off' indicates an anagram.
The alternating letters of 'some' are 'sm'.
'are'+'on'+'sm'='areonsm'
'areonsm' with letters rearranged gives 'OARSMEN'.
(Other definitions for oarsmen that I've seen before include "People in boats" , "They row the boat" , "Crew - moaners (anag)" , "They propel a boat manually" , "They propel boats manually" .)